The impulse created at each detonation is a significant contributor to the noise, vibration and harshness (NVH) of an internal combustion engine. Generally, a single cylinder engine produces greater NVH than a multi-cylinder engine of equal displacement. This is because a single cylinder engine produces a single detonation per engine revolution, whereas a multi-cylinder engine producing the same power spreads that power out over multiple detonations per revolution. This spread of power in multi-cylinder engines both reduces the magnitude of each detonation and increases the frequency of detonations, rendering them less noticeable.
However, multi-cylinder engines have the downside of having more moving parts and complexity. This increases frictional losses and cost, and provides slightly less power per unit of displacement.
Most engines have a flywheel attached to the crankshaft outside the combustion chamber that serves to smooth out the combustion cycle impulses and by storing energy to be used between detonations. When a ring gear, used for starting the engine, and/or a magneto, used for generating electricity, are present, the moments of inertia of these components are added to the moment of inertia of the flywheel. Greater moments of inertia of the flywheel and of components turning in the same direction as the flywheel result in greater smoothing out of the impulses created during the combustion cycle. However, even with such a flywheel, there remains unbalanced forces that cause NVH, including an unopposed couple on the engine block created by the cylinder side wall force.
There is therefore a need for an internal combustion engine assembly having a system for smoothing out the combustion cycle impulses.
There is also a need for a single cylinder engine assembly having such a system.